Field of the Invention

The present invention relates generally to inhibiting marine growth and, in particular, to inhibiting marine growth in an at least partially submersed or submerged watercraft or marine vessels.

Although the present invention will be described with particular reference to inhibiting marine growth in water jet propulsion units and bow thruster units which are installed on marine vessels such as boats, ships, . or the like, it will be appreciated that it is not limited to this use and that it may be used to inhibit marine growth on other parts of such vessels, or other watercraft or marine vessels which include a cavity and which are susceptible to fouling with marine growth. For example, it may be used to inhibit marine growth in other types of thruster units such as stern thruster units. It may also be used to inhibit marine growth in spaces containing retractable propulsion pods, viewing ports (in the case of glass bottom water craft or marine vessels), or control areas for foils and rudders of a watercraft or marine vessel.

Background Art

If a marine vessel such as, for example, a ship or boat sits idly in water for an extended period of time there can be a significant accumulation or build-up of marine growth on the surfaces of the hull and appendages (e.g. rudder) of the vessel. There can also be a significant build-up of marine growth within cavities in the hull of the vessel. Such accumulated material is commonly referred to as fouling, and its presence is undesirable. Other issues such as corrosion and erosion on marine vessels are also undesirable.

Fouling can adversely impact the performance of a marine vessel by causing it to operate inefficiently as it increases the marine vessel's frictional resistance to movement. If it is desired that a vessel with fouling perform at an optimum level, the fouled hull and appendages of the vessel must be cleaned so as to remove the fouling. Fouling can be particularly detrimental to high speed vessels because, due to the nature of these vessels, they can be very' sensitive to small changes in frictional resistance. Depending on the particular hull coating which has been applied to the outer hull of a marine vessel, the outer hull may be fouled with an accumulation of marine growth/microorganisms and/or other material as a result of the vessel not being operated for an extended period. However, in comparison to the removal of fouling from within cavities of a vessel, it is a relatively straightforward procedure to clean fouling from the outer hull of a vessel. This is due to the relative ease with which such parts of a vessel can normally be accessed as well as the quality of coatings that are usually applied to them.

It can be extremely difficult to clean some parts of a marine vessel such as the interior of some cavities of such a vessel. For example, the impeller blades within a water jet propulsion device or unit of a vessel may require mechanical scrubbing or cleaning with high pressure media in order to remove fouling such as marine growth from them. However, if the impeller blades are obstructed by stators of the propulsion unit and consequently cannot be readily accessed through the nozzle of the propulsion unit, specialists equipped with underwater breathing apparatus may have to dive beneath the vessel so that they can climb inside the inlet duct of the propulsion unit from below and clean the forward side of the impeller blades. (The aft sides cannot be accessed without special tools.) The vessel may need to be removed from the water so that the interior of the propulsion unit can be accessed without specialists having to firstly dive beneath the vessel to gain access to the inlet duct. When removed from the water, the water jets often need to be disassembled to provide access for full cleaning.

A known method of keeping the cavities of a marine vessel free from fouling such as marine growth involves removing the vessel from the water by means of slipping. Slipping a vessel or removing it from the water by other methods like dry-docking is traditionally a costly exercise. Also, storing large vessels out of the water for a period of time is costly and generally impractical. Some marine hull coatings also require to be kept wet which would necessitate re-application of the coating if the vessel was stored out of the water.

Cavities of marine vessels which are susceptible to fouling are often coated with an anti-fouling coating such as an anti-fouling paint which inhibits marine growth. However, where components that are located within these cavities are self-cleaning when the vessels on which they are stored are operating and not sitting idle, and/or they are coated with an ablative paint, such components cannot usually be coated with an anti-fouling coating and they are consequently susceptible to fouling if the vessel on which they are installed is sitting idly in water for an extended period of time.

A known method for performing maintenance and repair on sea chest main valves and other openings that penetrate the hull of a watercraft is to secure a cover over the opening and to pump the water out from behind this cover. The watertight boundary of the vessel is effectively shifted to this cover from the cavity itself. This method is difficult to perform for large areas with multiple openings such as water jet cavities. Also, the method is not practical or intended for inhibiting marine growth but is simply to allow maintenance to be performed. ^L -

It is against this background that the present invention has been developed.

Summary of the Invention

It is an object of the present invention to overcome, or at least ameliorate, one or more of the deficiencies of the prior art mentioned above, or to provide the consumer with a useful or commercial choice.

Other objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, a preferred embodiment of the, present invention is disclosed.

According to a first broad aspect of the present invention, there is provided a system for inhibiting marine growth or other fouling in a cavity of a watercraft which is at least partially submersed when the watercraft is sitting in water, the system including a cover for sealing an opening of the cavity such that water is inhibited from entering the cavity through the opening, and such that a displacing fluid that is introduced in to the cavity and that displaces water from the cavity is inhibited from escaping from the cavity through the opening.

Inhibiting water from entering the cavity and displacing the water in the cavity with a displacing fluid such that the displacing fluid is inhibited from leaving the cavity is able to inhibit microorganisms from growing inside the cavity and fouling it. It can also inhibit corrosion from fouling the cavity when the water in the cavity is replaced with a less corrosive media/fluid.

The system is particularly suitable for inhibiting marine growth or other fouling in a cavity that is located in a hull of the watercraft.

The watercraft may be any suitable watercraft. For example, the watercraft may be a marine vessel such as a boat, ship, or the like.

Preferably, the cover includes a plate for positioning over the opening such that a seal is able to be formed between the plate and the opening. The cover may also include one or more ratchet straps, fitting lugs, bolts, or clamps for securing the plate relative to the opening.

Preferably, the cover also includes a sealing member for forming a seal between the plate and the opening. The sealing member could, for example, be a gasket. The gasket could be an inflatable gasket. Alternatively, the sealing member could be a rubber seal.

Preferably, the system also includes a pump for pumping the displacing fluid in to the cavity such that the displacing fluid displaces the water from the cavity.

Preferably, the displacing fluid has a density that is less than the density of water. Alternatively, the displacing fluid has a density that is greater than the density of water.

Preferably, the displacing fluid is a pressurised gas. It is particularly preferred that the displacing fluid is pressurised/compressed and dried air.

Preferably, the system also includes a gauge for indicating/measuring the pressure of the displacing fluid in the cavity.

Preferably, the system also includes a control device/mechanism for controlling the pressure of the displacing fluid in the cavity/maintaining the pressure of the displacing fluid in the cavity at a desired pressure. The control device/mechanism may be part of the gauge.

Preferably, the system also includes an ultraviolet light source for emitting ultraviolet light within the cavity.

Preferably, the system also includes a heat source for heating the cavity.

Preferably, the system also includes a sensor for monitoring the cavity. For example, the system could include a camera for visually monitoring the cavity, and/or a temperature sensor for monitoring the temperature within the cavity.

In one preferred arrangement, the cavity is a cavity of a water jet propulsion unit, the cover is for sealing one of an intake opening and an outlet opening of the propulsion unit such that water is inhibited from entering the cavity through the sealed one of the intake opening and outlet opening, wherein the displacing fluid is able to be introduced in to the cavity such that water in the cavity is displaced from the cavity through the unsealed one of the intake opening and outlet opening.

Alternatively there may be two or more covers over the various openings of the cavity where at least one of the openings is left unsealed, wherein the displacing fluid is able to be introduced in to the cavity such that water in the cavity is displaced from the cavity through the at least one unsealed opening.

The water jet propulsion unit may be of any suitable type. For example, the water jet propulsion unit may be a mixed flow water jet propulsion unit or an axial flow water jet propulsion unit.

Preferably, where the cover is for sealing the intake opening of the water jet propulsion unit such that water is inhibited from entering the cavity through the intake opening, the displacing fluid is able to be introduced in to the cavity such that water in the cavity is displaced from the cavity through the outlet opening.

Preferably, where the cover is for sealing the outlet opening of the water jet propulsion unit such that water is inhibited from entering the cavity through the outlet opening, the displacing fluid is able to be introduced in to the cavity such that water in the cavity is displaced from the cavity through the intake opening.

Preferably, the system also includes an inlet for introducing the displacing fluid in to the cavity of the water jet propulsion unit. Alternatively, the system also includes a conduit for introducing the displacing fluid in to the cavity of the water jet propulsion unit through the unsealed one of the intake opening and outlet opening.

In a further preferred arrangement, the cavity is a cavity of a thruster unit, the cover is for sealing the opening of the cavity such that water is inhibited from entering the cavity through the opening, and the system also includes a further cover for sealing a further opening of the cavity such that water is also inhibited from entering the cavity through the further opening, an outlet through which water in the cavity is able to be displaced from the cavity, and at least one inlet for introducing the fluid in to the cavity such that water in the cavity is able to be displaced from the cavity through the outlet by the displacing fluid.

Preferably, the system also includes a drain connected to the outlet. Preferably, the system also includes a one-way valve connected to the drain on the outlet.

According to a second broad aspect of the present invention, there is provided a method for inhibiting marine growth or other fouling in a cavity of a watercraft, the method including the steps of:

introducing a displacing fluid in to the cavity such that the displacing fluid displaces water from the cavity; and

sealing an opening of the cavity such that water is inhibited from entering the cavity through the opening, and such that the displacing fluid is inhibited from escaping from the cavity through the opening.

Preferably, the introducing step comprises pumping the displacing fluid in to the cavity.

Preferably, the displacing fluid has a density that is less than the density of Water. Alternatively, the displacing fluid has a density that is greater than the density of water.

Preferably, the displacing fluid is a pressurised gas. It is particularly preferred that the fluid is pressurised/compressed and dried air.

Preferably, the sealing step comprises sealing the opening with a cover.

Preferably, the method also comprises the step of controlling the pressure of the fluid in the cavity/maintaining the pressure of the fluid in the cavity at a desired pressure.

Preferably, the method also comprises the step of illuminating the interior of the cavity with ultraviolet light.

Preferably, the method also comprises the step of heating the interior of the cavity.

Preferably, the method also comprises the step of monitoring the interior of the cavity. For example, the method may also comprise the step of visually monitoring the interior of the cavity with a camera, and/or monitoring the temperature and/or humidity in the interior of the cavity with a sensor. ln one preferred form, the cavity is a cavity of a water jet propulsion unit of the watercraft, the opening is one of an intake opening and an outlet opening of the propulsion unit, and the step of introducing the displacing fluid in to the cavity is such that water is displaced from the cavity through the unsealed one of the intake opening and outlet opening.

Preferably, the displacing fluid is introduced in to the cavity through an inlet. Alternatively, the displacing fluid is introduced in to the cavity through a conduit that extends in to the conduit through the unsealed one of the intake opening and outlet opening.

In a further preferred form, the cavity is a cavity of a thruster unit of the watercraft, the opening comprises a first opening of the cavity and a second opening of the cavity, the step of introducing the displacing fluid in to the cavity is such that water is displaced from the cavity through art outlet, and the step of sealing the opening comprises sealing the first opening and the second opening.

According to a third broad aspect of the present invention, there is provided a watercraft including a system according to the first broad aspect of the present invention.

According to a fourth broad aspect of the present invention, there is provided a cover of a system according to the first broad aspect of the present invention.

Preferably, the cover includes a plate for positioning over the opening such that a seal is able to be formed between the plate and the opening.

Preferably, the cover also includes one or more ratchet straps, fitting lugs, bolts, or clamps for securing the plate relative to the opening.

Preferably, the cover also includes a sealing member for forming a seal between the plate and the opening. The sealing member could, for example, be a gasket. The gasket could be an inflatable gasket. Alternatively, the sealing member could be a rubber seal.

Preferably, the cover includes an inlet for introducing the displacing fluid in to the cavity.

Preferably, the cover includes a gauge for indicating/measuring the pressure of the fluid in the cavity. Preferably, the cover includes a control device/mechanism for controlling the pressure of the displacing fluid in the cavity/maintaining the pressure of the displacing fluid in the cavity at a desired pressure.

Preferably, the cover includes an outlet through which water in the cavity is able to be displaced from the cavity.

Preferably, the cover includes a drain connected to the outlet.

Preferably, the cover includes a one-way valve connected to the outlet.

According to a fifth broad aspect of the present invention, there is provided a water jet propulsion unit for a watercraft, the water jet propulsion unit including a cavity which is at least partially submersed when the watercraft is sitting in water, and which includes an intake opening and an outlet opening, and a cover for sealing one of the intake opening and outlet opening such that water is inhibited from entering the cavity through the sealed one of the intake opening and outlet opening, and such that a displacing fluid that is introduced in to the cavity and that displaces water from the cavity through the unsealed one of the intake opening and outlet opening is inhibited from escaping from the cavity through the sealed one of the intake opening and outlet opening.

In one preferred form, the water jet propulsion unit is of the mixed flow jet type. In another preferred form, the water jet propulsion unit is of the axial flow jet type.

According to a sixth broad aspect of the present invention, there is provided a method of inhibiting marine growth or other fouling in a cavity of a water jet propulsion unit for a watercraft, the method, including the step of sealing one of an intake opening and an outlet opening of the cavity such that water is inhibited from entering the cavity through the sealed one of the intake opening and outlet opening, and such that a displacing fluid that is introduced in to the cavity and that displaces water from the cavity through the unsealed one of the intake opening and outlet opening is inhibited from escaping from the cavity through the sealed one of the intake opening and outlet opening.

According to a seventh broad aspect of the present invention, there is provided a thruster unit for a watercraft, the thruster unit including a cavity which is normally at least partially submersed when the watercraft is sitting in water, and which includes a first opening and a second opening, a first cover, and a second cover, the first cover for sealing the first opening and the second cover for sealing the second opening such that water is inhibited from entering the cavity through either of the first opening and the second opening, and such that a displacing fluid that displaces water from the cavity is inhibited from escaping from the cavity through either of the first opening and the second opening.

Preferably, the thruster unit is a bow thruster unit.

According to an eighth broad aspect of the present invention, there is provided a method of inhibiting marine growth in a cavity of a thruster unit for a watercraft, the method including the steps of sealing a first opening of the cavity with a first cover, and sealing a second opening of the cavity with a second cover such that water is inhibited from entering the cavity through either of the first opening and the second opening, and such that a displacing fluid that displaces water from the cavity is inhibited from escaping from the cavity through either of the first opening and the second opening.

According to a ninth broad aspect of the present invention, there is provided a method of inhibiting marine growth in a watercraft cavity which has multiple openings, the method including the steps of sealing at least one of the openings with a cover such that water that water is inhibited from entering the cavity through the at least one sealed opening, and leaving at least one of the openings unsealed so that water in the cavity is able to be displaced from the cavity through the at least one unsealed opening by a displacing fluid.

Brief Description of the Drawings

In order that the invention may be more fully understood and put into practice, a preferred embodiment thereof will now be described with reference to the accompanying drawings, in which:

Figure 1 is a partial cross-sectional side elevation of a starboard side of a marine vessel hull that includes a system for inhibiting fouling of a water jet propulsion unit of the vessel, and a system for inhibiting fouling of a bow thruster unit of the vessel;

Figure 2 is a cross-sectional side elevation of a portion of the starboard side of the marine vessel hull which depicts the water jet propulsion unit of the vessel in greater detail; Figure 3 is a front elevation of the nozzle outlet cover which forms part of the system for inhibiting fouling of the water jet propulsion unit depicted in figure

2;

Figure 4 is a side elevation of the nozzle cover;

Figure 5 is a cross-sectional front elevation of the bow of the vessel hull depicted in figure 1 which depicts the bow thruster unit of the vessel; and

Figure 6 is a cross-sectional side elevation of the starboard side of another marine vessel hull which depicts a water jet propulsion unit which is installed on the vessel, and a system for inhibiting fouling of the propulsion unit.

Best Mode(s) for Carrying out the Invention

In the drawings, like features of the various embodiments are referenced with like reference numbers.

Referring to figure 1 , there is depicted a watercraft/marine vessel 20 that includes a hull 21. The marine vessel 20 may, for example, be a boat or a ship.

Hull 21 includes a body 22, a bow thruster unit 23, and a water jet propulsion unit 24. Both the bow thruster unit 23 and the water jet propulsion unit 24 are installed in the body 22. The bow thruster unit 23 is located near the front/ bow of the hull 21 and beneath a normal/original waterline 25 of the vessel 20. The water jet propulsion unit 24 is situated at the rear/stern of the hull 21 such that a cavity 26 of the propulsion unit 24 is at least partially located beneath the waterline 25 which corresponds to the waterline of the vessel 20 when the vessel 20 is at rest. It can be seen that the at-rest waterline 25 is roughly in the middle of the cavity 26.

Referring to figure 2, the water jet propulsion unit 24 includes a duct 27 that extends from a bottom surface 28 of the hull body 22 to a rear surface 29 of the hull body 22. The propulsion unit 24 also includes a nozzle 30 that is joined to the duct 27. The duct 27 and the nozzle 30 define the cavity 26 of the propulsion unit 24 which extends from an intake opening 31 of the unit 24 which is defined by the duct 27 to an outlet opening 32 of the unit 24 which is defined by the nozzle 30. It can be seen that the nozzle outlet opening 32 is higher than the intake opening 31 which is not fitted with a cover.

The water jet propulsion unit 24 also includes an impeller (not visible) which is located within the nozzle 30 and which is secured to a rotatable drive shaft 33 such that rotation of the drive shaft 33 rotates the impeller relative to the nozzle 30. The drive shaft 33 is coupled to an engine (not depicted) of the vessel 20 such that the engine is able to rotate the shaft 33. The rotating impeller functions to draw water into the duct 27 through the intake opening 31 in the bottom 28 of the hull body 22, and to then expel the water as a jet from the outlet opening 32 of the nozzle 30. The expelled water imparts a force on the hull 21 which pushes the vessel 20 forward.

If the vessel 20 sits idly in water for an extended period of time, the interior of the cavity 26 of the water jet propulsion unit 24 may become fouled with microorganisms, corrosion, and/or other foreign matter/material that may adversely affect the performance of the propulsion unit 24 and, therefore, the vessel 20.

The impeller of the propulsion unit 24 is particularly susceptible to fouling because it is normally not coated with an anti-fouling coating or paint due to the fact that it is generally able to clean itself when in operation. However, if the water jet propulsion unit 24 also includes a stator (not depicted) situated inside the nozzle 30, the stator may obstruct access to the impeller through the nozzle outlet opening 32 and thereby make it extremely difficult to properly clean the impeller through the outlet opening 32 by scrubbing it or using a high pressure cleaning device.

As a consequence of the impeller being inaccessible for cleaning through the nozzle outlet opening 32, it is necessary for a person to insert themselves into the duct 27 so that they can properly clean the interior of the propulsion unit 24, including its impeller. If the vessel 20 is sitting in the water, it must be lifted out of the water so that the person can enter the duct 27 through the intake opening 31. Alternatively, instead of lifting the vessel 20 out of the water, the person must use underwater breathing apparatus so that they can dive into the water beneath the vessel 20 and then climb inside the duct 27 through the intake opening 31.

The vessel 20 includes a system 40 for inhibiting the interior of the cavity

26 of the water jet propulsion unit 24, including the impeller, from being fouled by marine growth, including microorganisms, and/or other matter/material such as, for example, corrosion. The system 40 includes a cover 41 (see also figures 3 and 4) for sealing the outlet opening 32 of the nozzle 30. The cover 41 includes a circular plate 42 and a plurality of ratchet straps 43 that are used to secure the plate 42 relative to the nozzle 30. In use, the plate 42 is positioned over the nozzle outlet opening 32, and the ratchet straps 43 are then operated to secure the plate 42 relative to the nozzle 30 such that a seal is formed between the plate 42 and the nozzle 30 around the outlet opening 32.

The system 40 also includes an inlet 50 that is secured to an internal inspection cover plate 51 that seals an inspection port 52 of the duct 27. The inlet 50 is for injecting a displacing fluid in to the cavity 26.

In addition, the system 40 includes a pressure gauge 53 for providing a visual indication of the pressure of the displacing fluid injected in to the cavity 26. The pressure gauge 53 can include a control mechanism to maintain the fluid in the cavity 26 at a desired pressure.

In use, a displacing fluid such as a marine growth inhibiting fluid in the form of a pressurised gas such as, for example, compressed air is injected/pumped/introduced in to the cavity 26 through the inlet 50 after the nozzle outlet opening 32 has been sealed with the cover 41. The injected displacing fluid substantially displaces water from the cavity 26 through the intake opening 31 so that the height of the water within the cavity 26 is lowered as indicated by the arrow 60. The displacing fluid is injected in to the cavity 26 so that the water in the cavity 26 has a new lower water line level 61. The control mechanism of the pressure gauge 53 controls the pressure of the displacing fluid in the cavity 26 to maintain the level 6 . If the displacing fluid leaks out of the cavity 26, the control mechanism would operate to allow more displacing fluid in to the cavity 26 to compensate for the leaked displacing fluid.

The lowering of the waterline within the cavity 26 from the waterline level

25 to the level 61 results in components in the cavity 26 such as the impeller being removed from the water. This inhibits organisms in the water, and particularly microorganisms in the water, from attaching themselves to the components (e.g. the impeller) which are no longer immersed in the water.

Referring to figure 5, the bow thruster unit 23 includes a circular cavity 70 that extends laterally through the hull body 22 and that is defined by a wall 71 of the hull body 22. A rotatable impeller 72 is housed within the cavity 70 as shown such that the impeller 72 is able to rotate relative to the body 22. The impeller 72 is coupled to a motor (not depicted) which is able to rotate the impeller 72. A respective circular opening 73 is located at each end of the cavity 70. Both openings 73 are located on the same level relative to the waterline level 25. The impeller 72 is operable to draw water in to the cavity 70 through either one of the openings 73, and to force or expel water out of the cavity 70 through the other one of the openings 73 so as to thereby exert a sideways/lateral force on the hull 21 which is able to move the vessel 20 sideways/laterally. The particular opening 73 through which the impeller 72 is able to draw water in to the cavity 70 and the particular opening 73 through which the impeller 72 is able to expel water out of the cavity 70 is dependent upon the direction of rotation of the impeller 72.

The vessel 20 also includes a system 80 for inhibiting the interior of the cavity 70, including the impeller 72, from being fouled by marine growth, including microorganisms, and/or other matter/material such as, for example, corrosion. The system 80 includes a pair of covers 81 (i.e. a first cover 81 and a second cover 81) for sealing the openings 73. Each cover 81 includes a plate 82 that is able to be secured relative to the hull body 22 such that a seal is formed between the plate 82 and the body 22 around either one of the openings 73. One of the covers 81 also includes an outlet 83 which includes a drain/drain pipe 84 that extends from the outlet 83.

The system 80 also includes an inlet 90 that is secured relative to the hull body wall 71 that defines the cavity 70 such that the inlet 90 communicates with the cavity 70. The inlet 90 is for injecting a displacing fluid such as, for example, a marine growth inhibiting fluid in to the cavity 70.

In addition, the system 80 includes a pressure gauge 91 for providing a visual indication of the pressure of the displacing fluid injected in to the cavity 70. The pressure gauge 91 can include a control mechanism to maintain the displacing fluid in the cavity 70 at the desired pressure.

In use, a displacing fluid such as, for example, compressed air is injected or pumped in to the cavity 70 through the inlet 90 after the openings 73 have been sealed with the covers 81. The injected displacing fluid displaces water from the cavity 70 through the drain 84 so that the height of the water within the cavity 70 is lowered to a level 61. The control mechanism of the pressure gauge 91 controls the pressure of the displacing fluid in the cavity 70 to maintain the level 61. If displacing fluid leaks out of the cavity 70, the control mechanism operates to allow more displacing fluid in to the cavity 70 to compensate for the leaked displacing fluid.

The cover 81 that includes the drain 84 is secured relative to the hull body 22 such that the drain 83 extends to a point which is below the level 61 in the cavity 70 that the water level in the cavity is required to fall to or below. This effectively moves the covered opening 73 to a lower point.

The lowering of the waterline within the cavity 70 from the waterline level 25 to the level 61 results in components in the cavity 70 such as the impeller 72 being removed from the. water. This inhibits organisms in the water, and particularly microorganisms in the water, from attaching themselves to the components (e.g. the impeller 72) which are no longer immersed in the water.

Instead of or in addition to including the drain 84, the outlet 83 could include a one-way valve such as, for example, a non-return valve (not depicted) so that fluid is able to flow through the outlet 83 in one direction (i.e. out of the cavity 70).

Another marine vessel 20 that includes a water jet propulsion device/unit 24 is shown in figure 6. The propulsion device 24 depicted in figure 6 is somewhat different to the propulsion device/unit illustrated in figure 2 in that one (i.e. the propulsion device depicted in figure 2) is a mixed flow jet and the other (i.e. the propulsion device depicted in figure 6) is an axial flow jet. The propulsion device 24 depicted in figure 6 has some items/components removed to simplify the depiction of the internal workings of the device 24.

The propulsion device 24 depicted in figure 6 includes an impeller 100 that is secured to the rotatable drive shaft 33 of the device 24 such that the impeller 100 rotates with the drive shaft 33. The propulsion device 24 also includes a stator 101 that is located inside the nozzle 30 and that is secured relative to the nozzle 30. It can be seen that the stator 101 inhibits access to the impeller 100 through the nozzle outlet opening 32, thus making it difficult to clean the impeller 100 through the outlet opening 32.

The vessel 20 depicted in figure 6 also includes a system 40 for inhibiting the interior of the cavity 26 of the propulsion device 24, including the impeller 100 and the stator 101, from being fouled by marine growth, including microorganisms, and/or other matter/material such as, for example, corrosion.

The system 40 is similar to the system depicted in figure 2 in that it includes a cover 41 that is for sealing the nozzle outlet opening 32, and that includes a plate 42. In use, the plate 42 is positioned over the nozzle outlet opening 32, and is then secured relative to the nozzle 30 such that a seal is formed between the plate 42 and the nozzle 30 around the outlet opening 32.

The system 40 depicted in figure 6 also includes an inlet 50 that is secured to an internal inspection cover plate 51 that seals an inspection port 52 of the duct 27. The inlet 50 is for injecting a displacing fluid in to the cavity 26. The displacing fluid may, for example, be a marine growth inhibiting fluid.

In addition, the system 40 depicted in figure 6 includes a pressure gauge 53 for providing a visual indication of the pressure of the displacing fluid injected in to the cavity 26. The pressure gauge 53 can also include a control mechanism for maintaining the displacing fluid in the cavity 26 at the desired pressure.

In use, a displacing fluid such as, for example, compressed air is injected or pumped in to the cavity 26 through the inlet 50 after the nozzle outlet opening 32 has been sealed with the cover 41. The injected displacing fluid substantially displaces water from the cavity 26 through the intake opening 31 so that the height of the water within the cavity 26 is lowered to a new lower water line 61.

In each of the above-described arrangements, water is removed from contact with the components (e.g. impeller) within the cavity 26, 70. Removing the water from contact with those components is able to prevent or at least inhibit those components from being fouled by marine growth. The reason for this is that removal/displacement of water from the cavities 26, 70 means that in those areas where the water has been removed, there is no longer a suitable medium for the marine growth to develop in.

In other embodiments, instead of being attached/secured to components/parts (e.g. cover plate 51 , hull body wall 71) of the cavities 26, 70, the inlets 50 and 90 for the displacing fluid, gauges 53 and 91 , and control mechanisms or control devices for controlling the pressure of the displacing fluid inside the cavities 26, 70 could be attached/secured to the covers 41 , 81 themselves, and, in particular, the plates 42, 82 of the covers 41 , 81.

In some arrangements, such as the arrangement depicted in figure 5 or 6, for example, it is not necessary to include fittings such as the inlets 50, 90 for introducing a displacing fluid (e.g. pressurised gas) in to the cavity 26, 70. Instead, one or more covers such as the covers 41 , 81 could be secured to the hull body 22 to completely seal the cavity 26, 70 while the vessel 20, or the part of the vessel 20 that includes the cavity 26, 70, is out of the water and after any water in the cavities 26, 70 has been drained therefrom and replaced with air. The vessel 20 or portion of the vessel 20 that is out of the water could then be re- introduced/re-inserted into the water. As the cavity 26, 70 is sealed by the cover(s) 41, 81 , this would pressurise the air in the cavity 26, 70 to the water pressure of the surrounding water.

Another alternative to using the inlet 50 to introduce the displacing fluid in to the cavity 26, is to simply run a conduit such as a gas line or pipe to the cavity 26 and to insert an end of the line in to the cavity 26 through the intake opening 31 after sealing the nozzle outlet opening 32 so that the displacing fluid is able to flow in to the cavity 26 from the conduit where it can then displace the water in the cavity 26 through the intake opening 31.

The system 40, 80 could include one or more additional fittings such as one or more additional inlet openings for introducing one or more additional fluids in to the cavity 26, 70. For example, one or more additional inlets 95 (see figure 2) could be secured relative to the cover plate 51 or the wall 71. The additional fluid(s), which could be aiding in the maintenance through rinsing and cleaning of the components (e.g. impeller) within the cavity 26, 70, could be sprayed directly on to the components within the cavity 26, 70 that are to be protected. The additional fluid could be a cleaning fluid that is able to clean minor growth which is accumulated on the vessel when it was being used, or to clean growth that may have occurred after the vessel ceased operation and before the system 40, 80 was installed and operated on the vessel to remove the water from the cavity 26, 70. Other fluids could include, for example, lanolin or similar substances to inhibit corrosion.

The system 40, 80 could include other fittings/components that allow for greater control of the conditions within the cavity 26, 70. These other fittings/components could include an ultraviolet light source for emitting ultraviolet light within the cavity 26, 70 so as to further control marine growth. They could also include a camera that could be located/positioned within the cavity 26, 70 and used for monitoring purposes. A heat source could be installed in the cavity 26, 70 to prevent freezing from occurring within the cavity 26, 70 in colder climates. Sensors for monitoring temperature and other conditions in the cavity 26, 70 could also be positioned in the cavity 26, 70.

The covers 41, 81 can be secured using various means and methods. For example, as already described, the ratchet straps 43 may be used to secure the cover 41 relative to the nozzle 30. Alternatively, the covers 41 , 81 could include fitting lugs for fitting inside the outlet opening 32 or openings 73 to enable the cover 41 , 81 to be clipped to the outlet opening 32 or opening 73. Another alternative is to secure the covers 41 , 81 with one or more bolts or clamps. A further alternative is to have the cover attached to the cavity opening with a hinge and to be hydraulically or otherwise locked into place.

The seal between the outlet opening 32 and openings 73 and the covers

41 , 81 can be achieved through various means and methods. For example, it could be achieved by having the mating surfaces of the cover 41 , 81 and nozzle

30 or hull body 22 machined in a manner that restricts the flow of water in to the cavity 26, 70 to a suitable level. The seal could be achieved by applying or inserting a gasket made from a suitable material between the outlet opening 32, opening 73 and the cover plate 42, 82 of the cover 41 , 81. The seal could be formed by an inflatable gasket. The covers 41 , 81 could include a rubber seal for sealing against the nozzle 30 or hull body 22, for example.

Where the displacing fluid that is introduced in to the cavity 26, 70 is a pressurised gas, it is preferred that the pressurised gas is compressed air owing to the ease of obtaining this gas. Other gases could be also introduced to displace the water. For example, a gas that is noxious to marine growth could be used, or an inert gas that prevents corrosion through oxidation could be used.

In another arrangement, the cavity 26, 70 may be filled with a displacing fluid whose density is different to the density of the fluid (e.g. water) in which the vessel 20 is floating. For example, if the displacing fluid is heavier than/more denser than the sea water in which the vessel 20 is floating, the intake opening

31 could be sealed by the cover 41 and the displacing fluid could be introduced in to the cavity 26 through the nozzle outlet opening 32. The displacing fluid would then displace the sea water out of the cavity 26 through the outlet opening 32.

A system which is similar to the system 40, 70 could be used to inhibit marine growth/fouling inside: a retractable bow thruster; a viewing port of a hull bottom, or regions around controllable appendages such as roll fins, for example. The system could be used on launch of a vessel to keep cavities of the vessel clean from marine growth.

The system 40, 80 as described is advantageous in that it is simple, cost-effective, and easy to install.

Installation of the system 40, 80 Is able to reduce or eliminate the amount of time that is required to clean marine growth. Currently, it takes approximately one day to clean a water jet using conventional methods that employ divers with specialised equipment.

Where the system 40, 80 uses compressed air as the displacing fluid, the air-supply can often be sourced from the vessel. Usually, only a power supply will be required to maintain intermittent operation of the air compressor.

It will be appreciated by those skilled in the art that variations and modifications to the invention described herein will be apparent without departing from the spirit and scope thereof. The variations and modifications. as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as herein set forth.

Throughout the specification and claims, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Throughout the specification and claims, unless the context requires otherwise, the term "substantially" or "about" will be understood to not be limited to the value for the range qualified by the terms.

It will be clearly understood that, if a prior art publication is referred to herein, that reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.